(1) Field of the Invention
The invention relates to mixing valves, and is directed more particularly to a valve for introducing a polymer into a stream of water prior to the flowing of the water and polymer mixture from an underwater vehicle and onto a hull surface thereof to reduce drag on the vehicle operating underwater.
(2) Description of the Prior Art
Drag created by the travel of underwater vehicles, caused by viscous effects of turbulent flow of water over exterior surfaces of the vehicle, limits the overall effectiveness and performance of such vehicles.
It is known to reduce such drag by delivering a stream of liquid polymer from inside the vehicle to the external hull surfaces of the vehicle, the polymer acting to reduce turbulance, and thereby reduce drag. A system for delivering polymer for such purpose is disclosed in U.S. patent application Ser. No. 08/083,222, filed Jun. 29, 1993, in the names of Pierre J. Corriveau et al.
The dispensed polymer, while effective to reduce drag, dissipates rather rapidly, being washed away by the water environment of the vehicle. Inasmuch as space is at a premium in such vehicles, the storage of large volumes of liquid polymer is not acceptable. Thus, if substantially pure polymer is dispensed, the time of its effectiveness is quite limited.
It is known that a slurry of water and liquid polymer, including a very small quantity of polymer in the slurry, such as 8 to 30 parts per million, is quite effective for the purpose. In view of this, the use of mixing valves for mixing together a small amount of polymer and a relatively large amount of water (taken from the water environment and therefore requiring no storage room) is known. The polymer is stored under pressure and, upon release, discharges into a stream of flowing water. It has been found, for example, that running the water through a venturi and injecting polymer into the venturi allows the water and polymer to mix sufficiently to be effective. A spring loaded valve has been used to close off the polymer. Pressurizing the polymer opened the valve and reducing the pressured closed the valve. It has been found, however, that when the polymer pressure is reduced, a small amount of water sometimes enters the valve polymer opening, causing the polymer to solidify at the opening. When this happens, it is necessary to disassemble the valve to remove the clog.
Accordingly, there is a need for a mixing valve which facilitates shutting off polymer flow while the polymer is under sufficient pressure to preclude water entry into the polymer valve opening.